A 3GPP that establishes a technology standard of a 3rd generation mobile communication system has started a research into long term evolution/system architecture evolution (LTE/SAE) technology as part of an effort to optimize and improve performance of 3 GPP technologies from the end of 2004 in order to cope with various forums and new technologies associated with 4th generation mobile communication.
SAE that is progressed around 3GPP SA WG2 is a research into network technology to determine a structure of a network with an LTE work of a 3GPP TSG RAN and support mobility between model networks and one of key standardization issues of the 3GPP. This is a work for developing a 3GPP system to a system that supports various wireless access technologies based on an IP and the work has been progressed for the purpose of an optimized packet based system that minimizes a transmission delay with a further improved data transmission capability.
An SAE higher-level reference model defined in the 3GPP SA WG2 includes a non-roaming case and a roaming case of various scenarios, and a detailed content may be referred in TS 23.400a and TS 23.400b which are 3GPP standard documents. A network structure diagram of FIG. 1 shows schematic reconfiguration of the SAE higher-level reference model.
FIG. 1 is a structural diagram of an evolved mobile communication network.
One of largest features of the network structure of FIG. 1 is based on a 2 tier model of eNodeB of an evolved UTRAN and a gateway of a core network and although accurately coincides with each other, the eNodeB 20 has functions of NodeB and RNC of an existing UMTS system and the gateway has an SGSN/GGSN function of the existing system.
Another key feature is that a control plane and a user plane between an access network and the core network are exchanged to different interfaces. In the existing UMTS system, one lu interface exists between an RNC and an SGSN, while a mobility management entity (MME) 51 that undertakes processing of a control signal has a structure separated from a gateway (GW), and as a result, two interfaces of S1-MME and S1-U are respectively used. The GW includes a serving-gateway (hereinafter, referred to as ‘S-GW’) 52 and a packet data network gateway (hereinafter, referred to as ‘PDN-GW’ or ‘P-GW’) 53.
FIG. 2 is a diagram illustrating the relationship between (e)NodeB and Home (e)NodeB.
In the 3rd or 4th mobile communication system, an attempt to increase a cell capacity is continuously made in order to support a high-capacity service and a bidirectional service such as multimedia contents, streaming, and the like.
That is, as various large-capacity transmission technologies are required with development of communication and spread of multimedia technology, a method for increase a radio capacity includes a method of allocating more frequency resources, but there is a limit in allocating more frequency resources to a plurality of users with limited frequency resources.
An approach to use a high-frequency band and decrease a cell radius has been made in order to increase the cell capacity. When a cell having a small radius, such as a pico cell is adopted, a band higher than a frequency used in the existing cellular system may be used, and as a result, it is possible to transfer more information. However, since more base stations should be installed in the same area, higher cost is required.
In recent years, a Femto base station such as a Home (e)NodeB 30 has been proposed while making the approach to increase the cell capacity by using the small cell.
The Home (e)Node 30 has been researched based on a RAN WG3 of the 3GPP Home (e)NodeB and in recent years, the Home (e)NodeB 30 has been in earnest researched even in an SA WG.
The (e)NodeB 20 illustrated in FIG. 2 corresponds to a macro base station and the Home (e)NodeB 30 illustrated in FIG. 2 may correspond to the Femto base station. In the specification, (e)NodeB intends to be described based on terms of the 3GPP and (e)NodeB is used when NodeB and eNodeB are mentioned together. Further, Home (e)NodeB is used when Home NodeB and Home eNodeB are mentioned together.
Interfaces marked with dotted lines are used to transmit control signals among the (e)NodeB 20, the Home (e)NodeB 30, and an MME 510. In addition, interfaced marked with solid lines are used to transmit data of the user plane.
FIG. 3 illustrates a problem in prior art.
As illustrated in FIG. 3, traffic is overloaded or congested in an interface between the (e)NodeB 20 and the S-GW 52, or traffic is overloaded or congested in an interface between the Home (e)NodeB 30 and the S-GW 52, download data or to a UE 10 or upload data from the UE 10 is not correctly transmitted and is thus failed.
Alternatively, even when an interface between the S-GW 52 and the PDN-GW 53 or an interface between the PDN-GW 53 and an Internet protocol (IP) service network of a mobile communication operator is overloaded or congested, the downlink data to the UE 10 or the uploaded data from the UE 10 is not correctly transmitted and is thus failed.
Further, when the UE is handed over from a present cell in which the UE receive a service to another cell, if the another cell is in an overload state, the service of the UE is dropped.
In order to solve the problem, mobile communication operators have changed the S-GW 52 and the PDN-GW 53 to high-capacity equipment or additionally installed new equipment, but very higher cost therefor is required. Further, the amount of transmitted and received data geometrically increases with each passing day, overload occurs immediately.
Meanwhile, various schemes were presented, which optimize the S-GW 52 and the PDN-GW 53 without additionally installing the mobile communication network. For example, SIPTO, that is, technology was presented, which transmits specific IP traffic (for example, an Internet service) of the UE by selecting an optimal route in a macro access network and offloads the IP traffic to a route through nodes of not the mobile communication network but a public network, that is, a wired network (selected IP traffic offload) without transmitting and receiving the IP traffic to and from the route through the mobile communication network in a Femto access network (for example, Home (e)NB).
FIG. 4 illustrates a concept of selected IP traffic offload (SIPTO).
Referring to FIG. 4, for example, a mobile communication system such as an evolved packet system (EPS) is illustrated. The EPS system includes the (e)NodeB 20, the MME 51, the S-GW 52, and a P-GW 53. In addition, the home (e)NodeB 30 is illustrated.
In this case, as illustrated, the selected IP traffic offload (SIPTO) technology offloads specific IP traffic (for example, an Internet service) of the UE 10 to nodes of a wired network 70 without passing through nodes in an IP service network 60 of a mobile communication operator.
For example, when the UE 10 is allowed to access the (e)NodeB 20, the UE 10 creates a session passing through the wired network 70 such as a public communication network through the (e)NodeB 20 and may perform an IP network service through the session. In this case, a operator policy and subscription information may be considered.
In order to create the session as such, a gateway, that is, a local gateway that undertakes some of functions of a GGSN in a UMTS or a local gateway that undertakes some of functions of a PDN gateway (P-GW) in an EPS may be installed at a location which is close to the (e)NodeB 20.
The local gateway is called a local GGSN or a local P-GW. A function of the local GGSN or local P-GW is similar to the function of the GGSN or P-GW.
As described above, the SIPTO technology has presented a concept of creating a session in order to offload the data of the UE to the wired network such as the public communication network through the (e)NodeB 20, that is, the macro base station.
However, the SIPTO technology in prior art has a problem that mobility is not assured. That is, when the UE performs handover from a source base station to a target base station while receiving an SIPTO service, cut-off of the service occurs.
For example, when the terminal performs handover to the Home (e)NodeB 30 during using the Internet by receiving the SIPTO service through the (e)NodeB 20, that is, the macro base station, data which the UE is transmitting is all lost and an Internet browser of the UE does not respond. Therefore, user's experience deteriorates.
In prior art described above, a scheme is presented, which creates a session for the data in order to offload the data of the UE to the wired network such as the public communication network when the UE stays at a geographically constant location for a long period.
However, the prior art does not consider movement of the UE. That is, the aforementioned prior art considers a situation in which the UE stays at the constant location similarly to wireless LAN technology.
However, the UE as a mobile terminal may frequently move or move long distances. Therefore, based on the aforementioned prior art, it is impossible to provide a service to a UE which is wide in movement range.